ABSTRACT. To identify evidence of essential fatty acid deficiency, we screened 64 patients with cystic fibrosis by analyzing total lipid extracts from plasma. Forty-three had an abnormal linoleate (18:2) level (less than 26%). Thirteen deficient patients (aged 10-24 yr) ingested for 1 yr 7% of their total calories as linoleate derived from a daily supplement of Microlipid. Five deficient patients (aged 10-37 yr) served as controls. Plasma and erythrocyte fatty acid composition were monitored by gas chromatography of total lipid extracts seven times during the twelve month period. Prostaglandins E2 and FZa and their 15 keto 13, 14 dihydrometabolite, 6-keto F,,, and thromboxane B2 were measured by radioimmunoassay. Sweat tests, oxygen saturation, growth indices, clinical severity scores, compliance, and possible side effects from taking Microlipid were followed. Results showed that oral supplementation with Microlipid can significantly increase plasma and erythrocytes %18:2. One compliant patient died during the study and had normal tissue 18:2 levels. Nine of 13 patients gained more weight while taking Microlipid than in the previous year. No significant changes in sweat electrolytes, clinical scores, or oxygen saturation were found during the study year. Prostaglandin metabolites prostaglandin E2 showed an upward trend in supplemented patients, compared to controls. Prostaglandin FZa remained unchanged over 1 yr but showed a trend significantly downward over the final 6 months in supplemented patients. We conclude that linoleate deficiency can be corrected with daily Microlipid supplements and that correction may alter prostaglandin metabolism (Pediatr Res 20: 36-41, 1986) Abbreviations CF, cystic fibrosis 18:2, linoleate PGM, 13,14-dihydro-15-PGFza PG, prostaglandin EFA, essential fatty acid RBC, red blood cells Several workers (1 -3) have demonstrated markedly decreased concentration of essential fatty acid (EFA) in plasma from CF patients. The major changes include a decreased level of the predominant EFA, linoleate (1 8:2), and increased palmitoleate

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